Hmm, it looks like you may be right. Good researching.
If you feel the epsom salts aren't helping, then I don't see anything wrong with trying aquarium salt. I would do a complete water change to get all the epsom salt out first. Fill the container back up to about half, then add the tsp of aquarium salt to the water you will put in the tank. Let the salt dissole a little, then add the water to his QT container. Try it and see if you notice any difference in his gill function. Also remember the website said to keep the water super clean, too, as toxins can make this worse.